Cat scratch disease, also known as cat scratch fever, or benign lymphoreticulosis, is a subacute localized granulomatous lymphadenitis caused by cat scratch infection, mostly in autumn and winter, mostly in children and young adults, and is the most common cause of chronic lymphadenopathy in children and young adults.
Cat scratch disease is caused by mostly Bartonella henselae and merely Bartonella quintana, which spread between cats and cats through fleas. The bacterium is transmitted to humans by cat scratches or bites. In areas with fleas, approximately 40% of cats have asymptomatic bacteremia.
Bartonella is a Gram-negative, oxidase-negative, aerobic bacterium. Bartonella can grow at 37 °C in blood culture medium containing 5% CO2, such as trypsin soy agar with 5% sheep blood, chocolate agar, and brain heart infusion agar, or in broth medium containing fetal bovine serum. Bartonella grows slowly in blood agar medium, and typical colony growth can be seen in 12 - 14 days, sometimes 45 days. The colonies are grayish white round protrusions with smooth or rough edges. The round craterlet is visible after the inoculation loop is scraped, which is an indication of Bartonella colonies growing in the medium. In the subculture stage, it is usually only 3 to 5 days to grow cloned colonies. Specimens suitable for the isolation of Bartonella include biopsy specimens of blood, lymphatic tissue, aspirate, skin, and other organs. For patients without other clinical symptoms, lymphatic specimens are superior to blood specimens. For patients with repeated fever, endocarditis, bacillary angiomatosis, peliosis hepatitis, and other systemic lesions, blood culture is better. Cell culture has also proven to be a valuable method for blood and lymphatic specimens.
Signs and Symptoms
3 - 7 days after cat scratches, one or multiple erythematous papules occur at the scratch sites, without obvious pain, some develop into vesicles or pustules, occasionally evolving into ulcers, crusting in 1 - 3 weeks, leaving temporary pigmentation after healing. Skin lesions are more common in the hands, forearms, feet, calves, face, and eyes, and can be ignored due to mild symptoms.
1 - 2 weeks after cat scratches, more than 90% of patients present with swollen draining lymph nodes, mainly in the head, neck, armpits, and groins, with solid texture, with mild tenderness, with a diameter of 1 - 8cm. 25% of patients develop purulent lymph nodes, occasionally with sinus tracts or fistulas. The enlarged lymph nodes usually resolve spontaneously within 2 to 4 months, and few persists for 6 to 24 months. Adjacent or even systemic lymph nodes may be enlarged.
Systemic symptoms are usually mild and are manifested by low fever, headache, chills, general malaise, discomfort, anorexia, nausea, vomiting, weight loss, splenomegaly, anginosis, and conjunctivitis, as well as thrombocytopenic purpura, osteomyelitis, endocarditis, encephalitis, meningitis, and cerebral arteritis, mostly in immunocompromised or AIDS patients.
Ocular symptoms are less common in cat scratch disease and are manifested by neuroretinitis, necrotizing conjunctivitis, conjunctivitis nodosa, follicular conjunctivitis, conjunctival hemangioma, hyalitis, anterior chamber inflammation, multifocal choroiditisretinal vasculitis, uveitis, retinopathies, and macular serous detachment.
Characteristic changes in lymph nodes are the formation of neutrophil microabscesses in the cortical and paracortical areas. The necrotic and purulent center and palisade periphery composed of epithelioid cells and megakaryocytes are present. In the involved lymph nodes, especially in the tissues surrounding small blood vessels, Gram-negative bacilli can be found with Warthin-starry stain.
The disease should be suspected when granulomatous nodules and unilateral lymphadenopathy occur after cat scratches.
Conjunctivitis accompanied by preauricular lymphadenopathy is one of the important features of cat scratch disease, which is helpful for diagnosis.
If the disease is suspected, a lymph node biopsy is feasible. Typical histopathological manifestations, such as suppurative granuloma, or detection of pathogens by immunofluorescence, can assist in the diagnosis.
Definitive diagnosis is based on the bacterial culture.
The disease is self-limiting, and most patients can spontaneously heal. Aspiration can be used in fluctuant lymph nodes, but incision and drainage are contraindicated. Patients with severe visceral disease or immunocompromised disease can be treated with rifampicin, erythromycin, clarithromycin, azithromycin, tetracycline, doxycycline, gentamicin, or ciprofloxacin. Severe swollen lymph nodes that cannot heal for a long time can be excised.
Fleas on the cat or in the environment should be controlled. Cat scratches or bites should be avoided.